Drilling predation on Permian brachiopods and bivalves from the Glass Mountains, west Texas ALAN P. HOFFMEISTER, MICHAŁ KOWALEWSKI, TOMASZ K. BAUMILLER, and RICHARD K. BAMBACH Hoffmeister, A.P., Kowalewski, M., Baumiller, T.K., and Bambach, R.K. 2004. Drilling predation on Permian brachio− pods and bivalves from the Glass Mountains, west Texas. Acta Palaeontologica Polonica 49 (3): 443–454. Although bored invertebrates have been described from every period of the Paleozoic, little information on the frequency and nature of Late Paleozoic drill holes exists. Our examination of the Permian silicified fossils, which were bulk col− lected by G.A. Cooper from the Glass Mountains of west Texas, revealed numerous drilled brachiopods and bivalve mol− lusks. Drill holes are perpendicular to the shell, smooth sided, sometimes beveled, and have other characteristics consis− tent with a predatory/parasitic origin. The frequency of drilling is significantly lower (p £0.05) for brachiopods (1.07%, n = 7597) than for bivalves (7.43%, n = 619). This study confirms that drilling predators and/or parasites were present in the Late Paleozoic. However, the drilling frequencies reported here—rarely exceeding 5%—are much lower than those reported for the Late Mesozoic and Cenozoic, which typically exceed 20%. The low Late Paleozoic frequencies are con− sistent with a majority of estimates reported previously for the older periods of the Paleozoic and suggest that the intensity of drilling predation/parasitism in marine benthic ecosystems remained low throughout the Paleozoic and did not increase until some time in the Mesozoic. Our data suggest that prey/host types with a higher nutritional return (bivalve mollusks) may have been preferentially selected for attack by predator(s)/parasites(s) already in the Permian. Key words: Drilling predation, drilling parasitism, Paleozoic, brachiopods, bivalve mollusks, Texas. Alan P. Hoffmeister [[email protected]] and Michal Kowalewski [[email protected]] Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA; current address of Alan P. Hoffmeister [[email protected]] Department of Physics, The College of New Jersey, P.O. Box 7718, Ewing, NJ 08628, USA; Tomasz K. Baumiller [[email protected]], Museum of Paleontology, University of Michigan, Ann Arbor, Michigan, 48109, USA; Richard K. Bambach [[email protected]], Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA, emeritus, and Botanical Museum, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA. Introduction Richards and Shabica 1969), it appears that at least some of the drillings observed in Paleozoic brachiopods are preda− The opportunity to study individual interactions in the fossil tory or parasitic in origin (e.g., Sheehan and Lesperance record and the chance to document a predator−prey system in 1978; Ausich and Gurrola 1979; Kowalewski et al. 2000; an evolutionary context has led to considerable interest in Leighton 2001; Hoffmeister et al. 2003). drilling predation. In particular, the hypothesis of escalation This study reports extensive quantitative data on drilling proposed by Vermeij (1987) can be tested rigorously using in Permian bivalves and brachiopods from West Texas as− drilled prey fossils both from the ecologic evolutionary per− sembled using the extensive Cooper collections housed in spective (e.g., Kelley and Hansen 1996) as well as from the the Smithsonian Institution National Museum of Natural point of view of functional morphology (e.g., Dietl et al. History. The Permian brachiopods and bivalves are a particu− 2000; Leighton 2001). However, most of the large−scale larly worthy target because the Late Paleozoic record of drill− quantitative studies to date have focused on the Cenozoic, a ing behavior has received very limited attention so far and time interval during which drilling predation has been a com− because there are very few reports of drilling predation in Pa− mon phenomenon (e.g., for recent reviews and numerous ref− leozoic bivalves (e.g., Kowalewski et al. 2000). erences see Kowalewski and Kelley 2002; Kelley et al. Based on a literature survey, Kowalewski et al. (1998) pro− 2003). In contrast, the record of drill holes is more controver− posed three distinct intervals in the history of drilling preda− sial for the Paleozoic (see Brett and Walker 2002; Baumiller tion. They suggested that this behavioral strategy was present and Gahn 2002; Brett 2003; Leighton 2003 and numerous throughout much of the Paleozoic, but noted that frequencies references therein). Whereas many of these drill holes may of drilling were much lower than those reported for the Late have been non−predatory in nature (e.g., substrate borings; Mesozoic and Cenozoic. Of particular interest is the “Meso− Acta Palaeontol. Pol. 49 (3): 443–454, 2004 http://app.pan.pl/acta49/app49−443.pdf 444 ACTA PALAEONTOLOGICA POLONICA 49 (3), 2004 Fig. 1. Study area. A. Location of Texas within the United States. B. Location of the city of Marathon with respect to other cities in Texas. C. Location of the Glass Mountains in the area of Marathon, Texas (modified from Cooper and Grant 1972). zoic Phase” (Permian–Early Cretaceous) characterized by behavior existed at some period in time, but of equal impor− very low drilling frequencies interpreted by Kowalewski et al. tance is to understand how drilling patterns changed through (1998) as a time interval when the predators were facultative time. This study examines strata from Texas that span much and only drilled rarely. However, this interval has very few re− of the Permian, thus allowing for investigation of temporal ported data points and this study aims to provide new insights trends within that time frame. into this under−researched time interval. The extensive quantitative dataset of Permian drill holes In addition, this project allows us to compare drilling pre− assembled here allows us to compare these new and more rig− dation between two morphologically and ecologically simi− orous estimates with the limited data published previously. lar groups that differ notably in various aspects of their biol− Kowalewski et al. (2000) provide data on drilling predation ogy and have had very disparate evolutionary histories. The for bivalve mollusks from Permian strata in the Paraná Basin desirability of such a comparison has long been recognized of Brazil, but these are limited only to a few controversial drill (e.g., Thayer 1981), yet we know of no direct comparison of holes. They also offered monographic estimates of predation drilling intensities between contemporaneous bivalves and rates on Permian brachiopods of West Texas, based on a series brachiopods in the literature to date. This type of analysis is of papers published by Cooper and Grant (1972, 1974, 1975, especially important in understanding the Paleozoic drilling 1976a, b, 1977). Because we re−examine here bulk materials predator−prey systems. The differences in tissue mass (typi− from which the monographed specimens were acquired, a cally higher for bivalves), shell thickness (brachiopod shells comparison of monographic estimates of drilling intensity tend to be thinner), shell composition and structure (calcitic with quantitative bulk estimates will be possible. If reasonable for most brachiopods and often aragonitic or mixed for bi− estimates of drilling intensity can be gathered from the litera− valves), prey habitat (brachiopods are generally epifaunal ture, then valuable data can be gathered first in the library. whereas at least some Paleozoic bivalves were infaunal), and This would offer us an effective tool for identifying time inter− relative abundance in fossil assemblages (brachiopods tend vals and geographic localities most critical for enhancing our to dominate many fossil assemblages in the Paleozoic; but understanding of the history of drilling predation. see Cherns and Wright 2000), all may provide insights into Finally, the data reported here allow us to compare vari− the nature of driller−prey/host interactions. ous metrics used for describing drilling intensity. Drilling in− Most previous studies of Paleozoic drilling behavior have tensity can be described from the total of all specimens in an dealt with collections from a single locality, which represent assemblage/sample (e.g., Kelley and Hansen 1993; Kowa− short time frames (but see Alexander 1986 and Leighton lewski et al. 1998), by the drilling intensity computed for a 2001 for studies that do address predation through time). selected taxon (e.g., Harper et al. 1998), or by the percentage These studies are important because they show that drilling of taxa that display drill holes (e.g., Vermeij 1987). Nearly HOFFMEISTER ET AL.—PERMIAN DRILLING PREDATION 445 726o limestone shale sandstone 721u* conglomerate 702* Cathedral Mountain Fm. 702un, 703b* 702b 708u, 703bs 702d 723-1 733g Sullivan Peak 714y Member 728p 722h Poplar Tank 708e 725f Fm. Permian Member 707ha Hess Fm. Decie Ranch Bell Canyon Skinner Ranch/ 707a Member 714o 715 715i 719z 705 Appel Ranch 727g 705k Member 705m 706d 705s Lenox Hills Fm. 706b 742b 723w 723t Permian 701d Word Fm. 724u 701a Willis Ranch 724g Member 701 Neal Ranch Fm. 706e* 701q , 701p 701v 706 Fig. 2. Composite stratigraphic column of the Glass Mountains area with the approx− China Tank 706c imate location of samples shown. Both Member brachiopods and bivalve mollusks were 724g examined from sample localities marked 707e* with an *. Only bivalves were examined 726d+, 722g+ Pennsylvanian Gaptank Fm. 100 m from localities marked with a +, while Fm. 719x Road Canyon 726za* only brachiopods were examined from lo− 702c*, 703d calities indicated just by their number. all studies of drilling predation to date have employed only one of the metrics to describe drilling intensity, but see Materials and methods Kelley and Hansen (1993) for a study that employed two metrics. Understanding how to best present the data is essen− The Glass Mountains have been used as the standard section tial to avoid misrepresenting behavioral, ecological, and evo− for the Permian of West Texas because of the completeness lutionary patterns.